deparse.c

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/*-------------------------------------------------------------------------
 *
 * deparse.c
 *        Query deparser for postgres_fdw
 *
 * This file includes functions that examine query WHERE clauses to see
 * whether they're safe to send to the remote server for execution, as
 * well as functions to construct the query text to be sent.  The latter
 * functionality is annoyingly duplicative of ruleutils.c, but there are
 * enough special considerations that it seems best to keep this separate.
 * One saving grace is that we only need deparse logic for node types that
 * we consider safe to send.
 *
 * We assume that the remote session's search_path is exactly "pg_catalog",
 * and thus we need schema-qualify all and only names outside pg_catalog.
 *
 * We do not consider that it is ever safe to send COLLATE expressions to
 * the remote server: it might not have the same collation names we do.
 * (Later we might consider it safe to send COLLATE "C", but even that would
 * fail on old remote servers.)  An expression is considered safe to send only
 * if all collations used in it are traceable to Var(s) of the foreign table.
 * That implies that if the remote server gets a different answer than we do,
 * the foreign table's columns are not marked with collations that match the
 * remote table's columns, which we can consider to be user error.
 *
 * Portions Copyright (c) 2012-2013, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        contrib/postgres_fdw/deparse.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "postgres_fdw.h"

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/transam.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


/*
 * Global context for foreign_expr_walker's search of an expression tree.
 */
typedef struct foreign_glob_cxt
{
    PlannerInfo *root;          /* global planner state */
    RelOptInfo *foreignrel;     /* the foreign relation we are planning for */
} foreign_glob_cxt;

/*
 * Local (per-tree-level) context for foreign_expr_walker's search.
 * This is concerned with identifying collations used in the expression.
 */
typedef enum
{
    FDW_COLLATE_NONE,           /* expression is of a noncollatable type */
    FDW_COLLATE_SAFE,           /* collation derives from a foreign Var */
    FDW_COLLATE_UNSAFE          /* collation derives from something else */
} FDWCollateState;

typedef struct foreign_loc_cxt
{
    Oid         collation;      /* OID of current collation, if any */
    FDWCollateState state;      /* state of current collation choice */
} foreign_loc_cxt;

/*
 * Context for deparseExpr
 */
typedef struct deparse_expr_cxt
{
    PlannerInfo *root;          /* global planner state */
    RelOptInfo *foreignrel;     /* the foreign relation we are planning for */
    StringInfo  buf;            /* output buffer to append to */
    List      **params_list;    /* exprs that will become remote Params */
} deparse_expr_cxt;

/*
 * Functions to determine whether an expression can be evaluated safely on
 * remote server.
 */
static bool foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt);
static bool is_builtin(Oid procid);

/*
 * Functions to construct string representation of a node tree.
 */
static void deparseTargetList(StringInfo buf,
                  PlannerInfo *root,
                  Index rtindex,
                  Relation rel,
                  Bitmapset *attrs_used,
                  List **retrieved_attrs);
static void deparseReturningList(StringInfo buf, PlannerInfo *root,
                     Index rtindex, Relation rel,
                     List *returningList,
                     List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
                 PlannerInfo *root);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseStringLiteral(StringInfo buf, const char *val);
static void deparseExpr(Expr *expr, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
                         deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);


/*
 * Examine each restriction clause in baserel's baserestrictinfo list,
 * and classify them into two groups, which are returned as two lists:
 *  - remote_conds contains expressions that can be evaluated remotely
 *  - local_conds contains expressions that can't be evaluated remotely
 */
void
classifyConditions(PlannerInfo *root,
                   RelOptInfo *baserel,
                   List **remote_conds,
                   List **local_conds)
{
    ListCell   *lc;

    *remote_conds = NIL;
    *local_conds = NIL;

    foreach(lc, baserel->baserestrictinfo)
    {
        RestrictInfo *ri = (RestrictInfo *) lfirst(lc);

        if (is_foreign_expr(root, baserel, ri->clause))
            *remote_conds = lappend(*remote_conds, ri);
        else
            *local_conds = lappend(*local_conds, ri);
    }
}

/*
 * Returns true if given expr is safe to evaluate on the foreign server.
 */
bool
is_foreign_expr(PlannerInfo *root,
                RelOptInfo *baserel,
                Expr *expr)
{
    foreign_glob_cxt glob_cxt;
    foreign_loc_cxt loc_cxt;

    /*
     * Check that the expression consists of nodes that are safe to execute
     * remotely.
     */
    glob_cxt.root = root;
    glob_cxt.foreignrel = baserel;
    loc_cxt.collation = InvalidOid;
    loc_cxt.state = FDW_COLLATE_NONE;
    if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt))
        return false;

    /* Expressions examined here should be boolean, ie noncollatable */
    Assert(loc_cxt.collation == InvalidOid);
    Assert(loc_cxt.state == FDW_COLLATE_NONE);

    /*
     * An expression which includes any mutable functions can't be sent over
     * because its result is not stable.  For example, sending now() remote
     * side could cause confusion from clock offsets.  Future versions might
     * be able to make this choice with more granularity.  (We check this last
     * because it requires a lot of expensive catalog lookups.)
     */
    if (contain_mutable_functions((Node *) expr))
        return false;

    /* OK to evaluate on the remote server */
    return true;
}

/*
 * Check if expression is safe to execute remotely, and return true if so.
 *
 * In addition, *outer_cxt is updated with collation information.
 *
 * We must check that the expression contains only node types we can deparse,
 * that all types/functions/operators are safe to send (which we approximate
 * as being built-in), and that all collations used in the expression derive
 * from Vars of the foreign table.  Because of the latter, the logic is
 * pretty close to assign_collations_walker() in parse_collate.c, though we
 * can assume here that the given expression is valid.
 */
static bool
foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt)
{
    bool        check_type = true;
    foreign_loc_cxt inner_cxt;
    Oid         collation;
    FDWCollateState state;

    /* Need do nothing for empty subexpressions */
    if (node == NULL)
        return true;

    /* Set up inner_cxt for possible recursion to child nodes */
    inner_cxt.collation = InvalidOid;
    inner_cxt.state = FDW_COLLATE_NONE;

    switch (nodeTag(node))
    {
        case T_Var:
            {
                Var        *var = (Var *) node;

                /*
                 * If the Var is from the foreign table, we consider its
                 * collation (if any) safe to use.  If it is from another
                 * table, we treat its collation the same way as we would a
                 * Param's collation, ie it's not safe for it to have a
                 * non-default collation.
                 */
                if (var->varno == glob_cxt->foreignrel->relid &&
                    var->varlevelsup == 0)
                {
                    /* Var belongs to foreign table */
                    collation = var->varcollid;
                    state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
                }
                else
                {
                    /* Var belongs to some other table */
                    if (var->varcollid != InvalidOid &&
                        var->varcollid != DEFAULT_COLLATION_OID)
                        return false;

                    /* We can consider that it doesn't set collation */
                    collation = InvalidOid;
                    state = FDW_COLLATE_NONE;
                }
            }
            break;
        case T_Const:
            {
                Const      *c = (Const *) node;

                /*
                 * If the constant has nondefault collation, either it's of a
                 * non-builtin type, or it reflects folding of a CollateExpr;
                 * either way, it's unsafe to send to the remote.
                 */
                if (c->constcollid != InvalidOid &&
                    c->constcollid != DEFAULT_COLLATION_OID)
                    return false;

                /* Otherwise, we can consider that it doesn't set collation */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_Param:
            {
                Param      *p = (Param *) node;

                /*
                 * Collation handling is same as for Consts.
                 */
                if (p->paramcollid != InvalidOid &&
                    p->paramcollid != DEFAULT_COLLATION_OID)
                    return false;

                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_ArrayRef:
            {
                ArrayRef   *ar = (ArrayRef *) node;;

                /* Assignment should not be in restrictions. */
                if (ar->refassgnexpr != NULL)
                    return false;

                /*
                 * Recurse to remaining subexpressions.  Since the array
                 * subscripts must yield (noncollatable) integers, they won't
                 * affect the inner_cxt state.
                 */
                if (!foreign_expr_walker((Node *) ar->refupperindexpr,
                                         glob_cxt, &inner_cxt))
                    return false;
                if (!foreign_expr_walker((Node *) ar->reflowerindexpr,
                                         glob_cxt, &inner_cxt))
                    return false;
                if (!foreign_expr_walker((Node *) ar->refexpr,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * Array subscripting should yield same collation as input,
                 * but for safety use same logic as for function nodes.
                 */
                collation = ar->refcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_FuncExpr:
            {
                FuncExpr   *fe = (FuncExpr *) node;

                /*
                 * If function used by the expression is not built-in, it
                 * can't be sent to remote because it might have incompatible
                 * semantics on remote side.
                 */
                if (!is_builtin(fe->funcid))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) fe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If function's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (fe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         fe->inputcollid != inner_cxt.collation)
                    return false;

                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)
                 */
                collation = fe->funccollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_OpExpr:
        case T_DistinctExpr:    /* struct-equivalent to OpExpr */
            {
                OpExpr     *oe = (OpExpr *) node;

                /*
                 * Similarly, only built-in operators can be sent to remote.
                 * (If the operator is, surely its underlying function is
                 * too.)
                 */
                if (!is_builtin(oe->opno))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;

                /* Result-collation handling is same as for functions */
                collation = oe->opcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;

                /*
                 * Again, only built-in operators can be sent to remote.
                 */
                if (!is_builtin(oe->opno))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_RelabelType:
            {
                RelabelType *r = (RelabelType *) node;

                /*
                 * Recurse to input subexpression.
                 */
                if (!foreign_expr_walker((Node *) r->arg,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * RelabelType must not introduce a collation not derived from
                 * an input foreign Var.
                 */
                collation = r->resultcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_BoolExpr:
            {
                BoolExpr   *b = (BoolExpr *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) b->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_NullTest:
            {
                NullTest   *nt = (NullTest *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) nt->arg,
                                         glob_cxt, &inner_cxt))
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_ArrayExpr:
            {
                ArrayExpr  *a = (ArrayExpr *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) a->elements,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * ArrayExpr must not introduce a collation not derived from
                 * an input foreign Var.
                 */
                collation = a->array_collid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_List:
            {
                List       *l = (List *) node;
                ListCell   *lc;

                /*
                 * Recurse to component subexpressions.
                 */
                foreach(lc, l)
                {
                    if (!foreign_expr_walker((Node *) lfirst(lc),
                                             glob_cxt, &inner_cxt))
                        return false;
                }

                /*
                 * When processing a list, collation state just bubbles up
                 * from the list elements.
                 */
                collation = inner_cxt.collation;
                state = inner_cxt.state;

                /* Don't apply exprType() to the list. */
                check_type = false;
            }
            break;
        default:

            /*
             * If it's anything else, assume it's unsafe.  This list can be
             * expanded later, but don't forget to add deparse support below.
             */
            return false;
    }

    /*
     * If result type of given expression is not built-in, it can't be sent to
     * remote because it might have incompatible semantics on remote side.
     */
    if (check_type && !is_builtin(exprType(node)))
        return false;

    /*
     * Now, merge my collation information into my parent's state.
     */
    if (state > outer_cxt->state)
    {
        /* Override previous parent state */
        outer_cxt->collation = collation;
        outer_cxt->state = state;
    }
    else if (state == outer_cxt->state)
    {
        /* Merge, or detect error if there's a collation conflict */
        switch (state)
        {
            case FDW_COLLATE_NONE:
                /* Nothing + nothing is still nothing */
                break;
            case FDW_COLLATE_SAFE:
                if (collation != outer_cxt->collation)
                {
                    /*
                     * Non-default collation always beats default.
                     */
                    if (outer_cxt->collation == DEFAULT_COLLATION_OID)
                    {
                        /* Override previous parent state */
                        outer_cxt->collation = collation;
                    }
                    else if (collation != DEFAULT_COLLATION_OID)
                    {
                        /*
                         * Conflict; show state as indeterminate.  We don't
                         * want to "return false" right away, since parent
                         * node might not care about collation.
                         */
                        outer_cxt->state = FDW_COLLATE_UNSAFE;
                    }
                }
                break;
            case FDW_COLLATE_UNSAFE:
                /* We're still conflicted ... */
                break;
        }
    }

    /* It looks OK */
    return true;
}

/*
 * Return true if given object is one of PostgreSQL's built-in objects.
 *
 * We use FirstBootstrapObjectId as the cutoff, so that we only consider
 * objects with hand-assigned OIDs to be "built in", not for instance any
 * function or type defined in the information_schema.
 *
 * Our constraints for dealing with types are tighter than they are for
 * functions or operators: we want to accept only types that are in pg_catalog,
 * else format_type might incorrectly fail to schema-qualify their names.
 * (This could be fixed with some changes to format_type, but for now there's
 * no need.)  Thus we must exclude information_schema types.
 *
 * XXX there is a problem with this, which is that the set of built-in
 * objects expands over time.  Something that is built-in to us might not
 * be known to the remote server, if it's of an older version.  But keeping
 * track of that would be a huge exercise.
 */
static bool
is_builtin(Oid oid)
{
    return (oid < FirstBootstrapObjectId);
}


/*
 * Construct a simple SELECT statement that retrieves desired columns
 * of the specified foreign table, and append it to "buf".  The output
 * contains just "SELECT ... FROM tablename".
 *
 * We also create an integer List of the columns being retrieved, which is
 * returned to *retrieved_attrs.
 */
void
deparseSelectSql(StringInfo buf,
                 PlannerInfo *root,
                 RelOptInfo *baserel,
                 Bitmapset *attrs_used,
                 List **retrieved_attrs)
{
    RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
    Relation    rel;

    /*
     * Core code already has some lock on each rel being planned, so we can
     * use NoLock here.
     */
    rel = heap_open(rte->relid, NoLock);

    /*
     * Construct SELECT list
     */
    appendStringInfoString(buf, "SELECT ");
    deparseTargetList(buf, root, baserel->relid, rel, attrs_used,
                      retrieved_attrs);

    /*
     * Construct FROM clause
     */
    appendStringInfoString(buf, " FROM ");
    deparseRelation(buf, rel);

    heap_close(rel, NoLock);
}

/*
 * Emit a target list that retrieves the columns specified in attrs_used.
 * This is used for both SELECT and RETURNING targetlists.
 *
 * The tlist text is appended to buf, and we also create an integer List
 * of the columns being retrieved, which is returned to *retrieved_attrs.
 */
static void
deparseTargetList(StringInfo buf,
                  PlannerInfo *root,
                  Index rtindex,
                  Relation rel,
                  Bitmapset *attrs_used,
                  List **retrieved_attrs)
{
    TupleDesc   tupdesc = RelationGetDescr(rel);
    bool        have_wholerow;
    bool        first;
    int         i;

    *retrieved_attrs = NIL;

    /* If there's a whole-row reference, we'll need all the columns. */
    have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
                                  attrs_used);

    first = true;
    for (i = 1; i <= tupdesc->natts; i++)
    {
        Form_pg_attribute attr = tupdesc->attrs[i - 1];

        /* Ignore dropped attributes. */
        if (attr->attisdropped)
            continue;

        if (have_wholerow ||
            bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            deparseColumnRef(buf, rtindex, i, root);

            *retrieved_attrs = lappend_int(*retrieved_attrs, i);
        }
    }

    /*
     * Add ctid if needed.  We currently don't support retrieving any other
     * system columns.
     */
    if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
                      attrs_used))
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        appendStringInfoString(buf, "ctid");

        *retrieved_attrs = lappend_int(*retrieved_attrs,
                                       SelfItemPointerAttributeNumber);
    }

    /* Don't generate bad syntax if no undropped columns */
    if (first)
        appendStringInfoString(buf, "NULL");
}

/*
 * Deparse WHERE clauses in given list of RestrictInfos and append them to buf.
 *
 * baserel is the foreign table we're planning for.
 *
 * If no WHERE clause already exists in the buffer, is_first should be true.
 *
 * If params is not NULL, it receives a list of Params and other-relation Vars
 * used in the clauses; these values must be transmitted to the remote server
 * as parameter values.
 *
 * If params is NULL, we're generating the query for EXPLAIN purposes,
 * so Params and other-relation Vars should be replaced by dummy values.
 */
void
appendWhereClause(StringInfo buf,
                  PlannerInfo *root,
                  RelOptInfo *baserel,
                  List *exprs,
                  bool is_first,
                  List **params)
{
    deparse_expr_cxt context;
    int         nestlevel;
    ListCell   *lc;

    if (params)
        *params = NIL;          /* initialize result list to empty */

    /* Set up context struct for recursion */
    context.root = root;
    context.foreignrel = baserel;
    context.buf = buf;
    context.params_list = params;

    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();

    foreach(lc, exprs)
    {
        RestrictInfo *ri = (RestrictInfo *) lfirst(lc);

        /* Connect expressions with "AND" and parenthesize each condition. */
        if (is_first)
            appendStringInfoString(buf, " WHERE ");
        else
            appendStringInfoString(buf, " AND ");

        appendStringInfoChar(buf, '(');
        deparseExpr(ri->clause, &context);
        appendStringInfoChar(buf, ')');

        is_first = false;
    }

    reset_transmission_modes(nestlevel);
}

/*
 * deparse remote INSERT statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseInsertSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *targetAttrs, List *returningList,
                 List **retrieved_attrs)
{
    AttrNumber  pindex;
    bool        first;
    ListCell   *lc;

    appendStringInfoString(buf, "INSERT INTO ");
    deparseRelation(buf, rel);

    if (targetAttrs)
    {
        appendStringInfoString(buf, "(");

        first = true;
        foreach(lc, targetAttrs)
        {
            int         attnum = lfirst_int(lc);

            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            deparseColumnRef(buf, rtindex, attnum, root);
        }

        appendStringInfoString(buf, ") VALUES (");

        pindex = 1;
        first = true;
        foreach(lc, targetAttrs)
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            appendStringInfo(buf, "$%d", pindex);
            pindex++;
        }

        appendStringInfoString(buf, ")");
    }
    else
        appendStringInfoString(buf, " DEFAULT VALUES");

    if (returningList)
        deparseReturningList(buf, root, rtindex, rel, returningList,
                             retrieved_attrs);
    else
        *retrieved_attrs = NIL;
}

/*
 * deparse remote UPDATE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseUpdateSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *targetAttrs, List *returningList,
                 List **retrieved_attrs)
{
    AttrNumber  pindex;
    bool        first;
    ListCell   *lc;

    appendStringInfoString(buf, "UPDATE ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " SET ");

    pindex = 2;                 /* ctid is always the first param */
    first = true;
    foreach(lc, targetAttrs)
    {
        int         attnum = lfirst_int(lc);

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        deparseColumnRef(buf, rtindex, attnum, root);
        appendStringInfo(buf, " = $%d", pindex);
        pindex++;
    }
    appendStringInfoString(buf, " WHERE ctid = $1");

    if (returningList)
        deparseReturningList(buf, root, rtindex, rel, returningList,
                             retrieved_attrs);
    else
        *retrieved_attrs = NIL;
}

/*
 * deparse remote DELETE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDeleteSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *returningList,
                 List **retrieved_attrs)
{
    appendStringInfoString(buf, "DELETE FROM ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " WHERE ctid = $1");

    if (returningList)
        deparseReturningList(buf, root, rtindex, rel, returningList,
                             retrieved_attrs);
    else
        *retrieved_attrs = NIL;
}

/*
 * deparse RETURNING clause of INSERT/UPDATE/DELETE
 */
static void
deparseReturningList(StringInfo buf, PlannerInfo *root,
                     Index rtindex, Relation rel,
                     List *returningList,
                     List **retrieved_attrs)
{
    Bitmapset  *attrs_used;

    /*
     * We need the attrs mentioned in the query's RETURNING list.
     */
    attrs_used = NULL;
    pull_varattnos((Node *) returningList, rtindex,
                   &attrs_used);

    appendStringInfoString(buf, " RETURNING ");
    deparseTargetList(buf, root, rtindex, rel, attrs_used,
                      retrieved_attrs);
}

/*
 * Construct SELECT statement to acquire size in blocks of given relation.
 *
 * Note: we use local definition of block size, not remote definition.
 * This is perhaps debatable.
 *
 * Note: pg_relation_size() exists in 8.1 and later.
 */
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
    StringInfoData relname;

    /* We'll need the remote relation name as a literal. */
    initStringInfo(&relname);
    deparseRelation(&relname, rel);

    appendStringInfo(buf, "SELECT pg_catalog.pg_relation_size(");
    deparseStringLiteral(buf, relname.data);
    appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}

/*
 * Construct SELECT statement to acquire sample rows of given relation.
 *
 * SELECT command is appended to buf, and list of columns retrieved
 * is returned to *retrieved_attrs.
 */
void
deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
{
    Oid         relid = RelationGetRelid(rel);
    TupleDesc   tupdesc = RelationGetDescr(rel);
    int         i;
    char       *colname;
    List       *options;
    ListCell   *lc;
    bool        first = true;

    *retrieved_attrs = NIL;

    appendStringInfoString(buf, "SELECT ");
    for (i = 0; i < tupdesc->natts; i++)
    {
        /* Ignore dropped columns. */
        if (tupdesc->attrs[i]->attisdropped)
            continue;

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        /* Use attribute name or column_name option. */
        colname = NameStr(tupdesc->attrs[i]->attname);
        options = GetForeignColumnOptions(relid, i + 1);

        foreach(lc, options)
        {
            DefElem    *def = (DefElem *) lfirst(lc);

            if (strcmp(def->defname, "column_name") == 0)
            {
                colname = defGetString(def);
                break;
            }
        }

        appendStringInfoString(buf, quote_identifier(colname));

        *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
    }

    /* Don't generate bad syntax for zero-column relation. */
    if (first)
        appendStringInfoString(buf, "NULL");

    /*
     * Construct FROM clause
     */
    appendStringInfoString(buf, " FROM ");
    deparseRelation(buf, rel);
}

/*
 * Construct name to use for given column, and emit it into buf.
 * If it has a column_name FDW option, use that instead of attribute name.
 */
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root)
{
    RangeTblEntry *rte;
    char       *colname = NULL;
    List       *options;
    ListCell   *lc;

    /* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
    Assert(!IS_SPECIAL_VARNO(varno));

    /* Get RangeTblEntry from array in PlannerInfo. */
    rte = planner_rt_fetch(varno, root);

    /*
     * If it's a column of a foreign table, and it has the column_name FDW
     * option, use that value.
     */
    options = GetForeignColumnOptions(rte->relid, varattno);
    foreach(lc, options)
    {
        DefElem    *def = (DefElem *) lfirst(lc);

        if (strcmp(def->defname, "column_name") == 0)
        {
            colname = defGetString(def);
            break;
        }
    }

    /*
     * If it's a column of a regular table or it doesn't have column_name FDW
     * option, use attribute name.
     */
    if (colname == NULL)
        colname = get_relid_attribute_name(rte->relid, varattno);

    appendStringInfoString(buf, quote_identifier(colname));
}

/*
 * Append remote name of specified foreign table to buf.
 * Use value of table_name FDW option (if any) instead of relation's name.
 * Similarly, schema_name FDW option overrides schema name.
 */
static void
deparseRelation(StringInfo buf, Relation rel)
{
    ForeignTable *table;
    const char *nspname = NULL;
    const char *relname = NULL;
    ListCell   *lc;

    /* obtain additional catalog information. */
    table = GetForeignTable(RelationGetRelid(rel));

    /*
     * Use value of FDW options if any, instead of the name of object itself.
     */
    foreach(lc, table->options)
    {
        DefElem    *def = (DefElem *) lfirst(lc);

        if (strcmp(def->defname, "schema_name") == 0)
            nspname = defGetString(def);
        else if (strcmp(def->defname, "table_name") == 0)
            relname = defGetString(def);
    }

    /*
     * Note: we could skip printing the schema name if it's pg_catalog, but
     * that doesn't seem worth the trouble.
     */
    if (nspname == NULL)
        nspname = get_namespace_name(RelationGetNamespace(rel));
    if (relname == NULL)
        relname = RelationGetRelationName(rel);

    appendStringInfo(buf, "%s.%s",
                     quote_identifier(nspname), quote_identifier(relname));
}

/*
 * Append a SQL string literal representing "val" to buf.
 */
static void
deparseStringLiteral(StringInfo buf, const char *val)
{
    const char *valptr;

    /*
     * Rather than making assumptions about the remote server's value of
     * standard_conforming_strings, always use E'foo' syntax if there are any
     * backslashes.  This will fail on remote servers before 8.1, but those
     * are long out of support.
     */
    if (strchr(val, '\\') != NULL)
        appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
    appendStringInfoChar(buf, '\'');
    for (valptr = val; *valptr; valptr++)
    {
        char        ch = *valptr;

        if (SQL_STR_DOUBLE(ch, true))
            appendStringInfoChar(buf, ch);
        appendStringInfoChar(buf, ch);
    }
    appendStringInfoChar(buf, '\'');
}

/*
 * Deparse given expression into context->buf.
 *
 * This function must support all the same node types that foreign_expr_walker
 * accepts.
 *
 * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
 * scheme: anything more complex than a Var, Const, function call or cast
 * should be self-parenthesized.
 */
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
    if (node == NULL)
        return;

    switch (nodeTag(node))
    {
        case T_Var:
            deparseVar((Var *) node, context);
            break;
        case T_Const:
            deparseConst((Const *) node, context);
            break;
        case T_Param:
            deparseParam((Param *) node, context);
            break;
        case T_ArrayRef:
            deparseArrayRef((ArrayRef *) node, context);
            break;
        case T_FuncExpr:
            deparseFuncExpr((FuncExpr *) node, context);
            break;
        case T_OpExpr:
            deparseOpExpr((OpExpr *) node, context);
            break;
        case T_DistinctExpr:
            deparseDistinctExpr((DistinctExpr *) node, context);
            break;
        case T_ScalarArrayOpExpr:
            deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
            break;
        case T_RelabelType:
            deparseRelabelType((RelabelType *) node, context);
            break;
        case T_BoolExpr:
            deparseBoolExpr((BoolExpr *) node, context);
            break;
        case T_NullTest:
            deparseNullTest((NullTest *) node, context);
            break;
        case T_ArrayExpr:
            deparseArrayExpr((ArrayExpr *) node, context);
            break;
        default:
            elog(ERROR, "unsupported expression type for deparse: %d",
                 (int) nodeTag(node));
            break;
    }
}

/*
 * Deparse given Var node into context->buf.
 *
 * If the Var belongs to the foreign relation, just print its remote name.
 * Otherwise, it's effectively a Param (and will in fact be a Param at
 * run time).  Handle it the same way we handle plain Params --- see
 * deparseParam for comments.
 */
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;

    if (node->varno == context->foreignrel->relid &&
        node->varlevelsup == 0)
    {
        /* Var belongs to foreign table */
        deparseColumnRef(buf, node->varno, node->varattno, context->root);
    }
    else
    {
        /* Treat like a Param */
        if (context->params_list)
        {
            int         pindex = 0;
            ListCell   *lc;

            /* find its index in params_list */
            foreach(lc, *context->params_list)
            {
                pindex++;
                if (equal(node, (Node *) lfirst(lc)))
                    break;
            }
            if (lc == NULL)
            {
                /* not in list, so add it */
                pindex++;
                *context->params_list = lappend(*context->params_list, node);
            }

            appendStringInfo(buf, "$%d", pindex);
            appendStringInfo(buf, "::%s",
                             format_type_with_typemod(node->vartype,
                                                      node->vartypmod));
        }
        else
        {
            appendStringInfo(buf, "(SELECT null::%s)",
                             format_type_with_typemod(node->vartype,
                                                      node->vartypmod));
        }
    }
}

/*
 * Deparse given constant value into context->buf.
 *
 * This function has to be kept in sync with ruleutils.c's get_const_expr.
 */
static void
deparseConst(Const *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    Oid         typoutput;
    bool        typIsVarlena;
    char       *extval;
    bool        isfloat = false;
    bool        needlabel;

    if (node->constisnull)
    {
        appendStringInfo(buf, "NULL");
        appendStringInfo(buf, "::%s",
                         format_type_with_typemod(node->consttype,
                                                  node->consttypmod));
        return;
    }

    getTypeOutputInfo(node->consttype,
                      &typoutput, &typIsVarlena);
    extval = OidOutputFunctionCall(typoutput, node->constvalue);

    switch (node->consttype)
    {
        case INT2OID:
        case INT4OID:
        case INT8OID:
        case OIDOID:
        case FLOAT4OID:
        case FLOAT8OID:
        case NUMERICOID:
            {
                /*
                 * No need to quote unless it's a special value such as 'NaN'.
                 * See comments in get_const_expr().
                 */
                if (strspn(extval, "0123456789+-eE.") == strlen(extval))
                {
                    if (extval[0] == '+' || extval[0] == '-')
                        appendStringInfo(buf, "(%s)", extval);
                    else
                        appendStringInfoString(buf, extval);
                    if (strcspn(extval, "eE.") != strlen(extval))
                        isfloat = true; /* it looks like a float */
                }
                else
                    appendStringInfo(buf, "'%s'", extval);
            }
            break;
        case BITOID:
        case VARBITOID:
            appendStringInfo(buf, "B'%s'", extval);
            break;
        case BOOLOID:
            if (strcmp(extval, "t") == 0)
                appendStringInfoString(buf, "true");
            else
                appendStringInfoString(buf, "false");
            break;
        default:
            deparseStringLiteral(buf, extval);
            break;
    }

    /*
     * Append ::typename unless the constant will be implicitly typed as the
     * right type when it is read in.
     *
     * XXX this code has to be kept in sync with the behavior of the parser,
     * especially make_const.
     */
    switch (node->consttype)
    {
        case BOOLOID:
        case INT4OID:
        case UNKNOWNOID:
            needlabel = false;
            break;
        case NUMERICOID:
            needlabel = !isfloat || (node->consttypmod >= 0);
            break;
        default:
            needlabel = true;
            break;
    }
    if (needlabel)
        appendStringInfo(buf, "::%s",
                         format_type_with_typemod(node->consttype,
                                                  node->consttypmod));
}

/*
 * Deparse given Param node.
 *
 * If we're generating the query "for real", add the Param to
 * context->params_list if it's not already present, and then use its index
 * in that list as the remote parameter number.
 *
 * If we're just generating the query for EXPLAIN, replace the Param with
 * a dummy expression "(SELECT null::<type>)".  In all extant versions of
 * Postgres, the planner will see that as an unknown constant value, which is
 * what we want.  (If we sent a Param, recent versions might try to use the
 * value supplied for the Param as an estimated or even constant value, which
 * we don't want.)  This might need adjustment if we ever make the planner
 * flatten scalar subqueries.
 *
 * Note: we label the Param's type explicitly rather than relying on
 * transmitting a numeric type OID in PQexecParams().  This allows us to
 * avoid assuming that types have the same OIDs on the remote side as they
 * do locally --- they need only have the same names.
 */
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;

    if (context->params_list)
    {
        int         pindex = 0;
        ListCell   *lc;

        /* find its index in params_list */
        foreach(lc, *context->params_list)
        {
            pindex++;
            if (equal(node, (Node *) lfirst(lc)))
                break;
        }
        if (lc == NULL)
        {
            /* not in list, so add it */
            pindex++;
            *context->params_list = lappend(*context->params_list, node);
        }

        appendStringInfo(buf, "$%d", pindex);
        appendStringInfo(buf, "::%s",
                         format_type_with_typemod(node->paramtype,
                                                  node->paramtypmod));
    }
    else
    {
        appendStringInfo(buf, "(SELECT null::%s)",
                         format_type_with_typemod(node->paramtype,
                                                  node->paramtypmod));
    }
}

/*
 * Deparse an array subscript expression.
 */
static void
deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    ListCell   *lowlist_item;
    ListCell   *uplist_item;

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /*
     * Deparse referenced array expression first.  If that expression includes
     * a cast, we have to parenthesize to prevent the array subscript from
     * being taken as typename decoration.  We can avoid that in the typical
     * case of subscripting a Var, but otherwise do it.
     */
    if (IsA(node->refexpr, Var))
        deparseExpr(node->refexpr, context);
    else
    {
        appendStringInfoChar(buf, '(');
        deparseExpr(node->refexpr, context);
        appendStringInfoChar(buf, ')');
    }

    /* Deparse subscript expressions. */
    lowlist_item = list_head(node->reflowerindexpr);    /* could be NULL */
    foreach(uplist_item, node->refupperindexpr)
    {
        appendStringInfoChar(buf, '[');
        if (lowlist_item)
        {
            deparseExpr(lfirst(lowlist_item), context);
            appendStringInfoChar(buf, ':');
            lowlist_item = lnext(lowlist_item);
        }
        deparseExpr(lfirst(uplist_item), context);
        appendStringInfoChar(buf, ']');
    }

    appendStringInfoChar(buf, ')');
}

/*
 * Deparse a function call.
 */
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   proctup;
    Form_pg_proc procform;
    const char *proname;
    bool        use_variadic;
    bool        first;
    ListCell   *arg;

    /*
     * If the function call came from an implicit coercion, then just show the
     * first argument.
     */
    if (node->funcformat == COERCE_IMPLICIT_CAST)
    {
        deparseExpr((Expr *) linitial(node->args), context);
        return;
    }

    /*
     * If the function call came from a cast, then show the first argument
     * plus an explicit cast operation.
     */
    if (node->funcformat == COERCE_EXPLICIT_CAST)
    {
        Oid         rettype = node->funcresulttype;
        int32       coercedTypmod;

        /* Get the typmod if this is a length-coercion function */
        (void) exprIsLengthCoercion((Node *) node, &coercedTypmod);

        deparseExpr((Expr *) linitial(node->args), context);
        appendStringInfo(buf, "::%s",
                         format_type_with_typemod(rettype, coercedTypmod));
        return;
    }

    /*
     * Normal function: display as proname(args).
     */
    proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(node->funcid));
    if (!HeapTupleIsValid(proctup))
        elog(ERROR, "cache lookup failed for function %u", node->funcid);
    procform = (Form_pg_proc) GETSTRUCT(proctup);

    /* Check if need to print VARIADIC (cf. ruleutils.c) */
    if (OidIsValid(procform->provariadic))
    {
        if (procform->provariadic != ANYOID)
            use_variadic = true;
        else
            use_variadic = node->funcvariadic;
    }
    else
        use_variadic = false;

    /* Print schema name only if it's not pg_catalog */
    if (procform->pronamespace != PG_CATALOG_NAMESPACE)
    {
        const char *schemaname;

        schemaname = get_namespace_name(procform->pronamespace);
        appendStringInfo(buf, "%s.", quote_identifier(schemaname));
    }

    /* Deparse the function name ... */
    proname = NameStr(procform->proname);
    appendStringInfo(buf, "%s(", quote_identifier(proname));
    /* ... and all the arguments */
    first = true;
    foreach(arg, node->args)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        if (use_variadic && lnext(arg) == NULL)
            appendStringInfoString(buf, "VARIADIC ");
        deparseExpr((Expr *) lfirst(arg), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');

    ReleaseSysCache(proctup);
}

/*
 * Deparse given operator expression.   To avoid problems around
 * priority of operations, we always parenthesize the arguments.
 */
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   tuple;
    Form_pg_operator form;
    char        oprkind;
    ListCell   *arg;

    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);
    oprkind = form->oprkind;

    /* Sanity check. */
    Assert((oprkind == 'r' && list_length(node->args) == 1) ||
           (oprkind == 'l' && list_length(node->args) == 1) ||
           (oprkind == 'b' && list_length(node->args) == 2));

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /* Deparse left operand. */
    if (oprkind == 'r' || oprkind == 'b')
    {
        arg = list_head(node->args);
        deparseExpr(lfirst(arg), context);
        appendStringInfoChar(buf, ' ');
    }

    /* Deparse operator name. */
    deparseOperatorName(buf, form);

    /* Deparse right operand. */
    if (oprkind == 'l' || oprkind == 'b')
    {
        arg = list_tail(node->args);
        appendStringInfoChar(buf, ' ');
        deparseExpr(lfirst(arg), context);
    }

    appendStringInfoChar(buf, ')');

    ReleaseSysCache(tuple);
}

/*
 * Print the name of an operator.
 */
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
    char       *opname;

    /* opname is not a SQL identifier, so we should not quote it. */
    opname = NameStr(opform->oprname);

    /* Print schema name only if it's not pg_catalog */
    if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
    {
        const char *opnspname;

        opnspname = get_namespace_name(opform->oprnamespace);
        /* Print fully qualified operator name. */
        appendStringInfo(buf, "OPERATOR(%s.%s)",
                         quote_identifier(opnspname), opname);
    }
    else
    {
        /* Just print operator name. */
        appendStringInfo(buf, "%s", opname);
    }
}

/*
 * Deparse IS DISTINCT FROM.
 */
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;

    Assert(list_length(node->args) == 2);

    appendStringInfoChar(buf, '(');
    deparseExpr(linitial(node->args), context);
    appendStringInfoString(buf, " IS DISTINCT FROM ");
    deparseExpr(lsecond(node->args), context);
    appendStringInfoChar(buf, ')');
}

/*
 * Deparse given ScalarArrayOpExpr expression.  To avoid problems
 * around priority of operations, we always parenthesize the arguments.
 */
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    HeapTuple   tuple;
    Form_pg_operator form;
    Expr       *arg1;
    Expr       *arg2;

    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);

    /* Sanity check. */
    Assert(list_length(node->args) == 2);

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /* Deparse left operand. */
    arg1 = linitial(node->args);
    deparseExpr(arg1, context);
    appendStringInfoChar(buf, ' ');

    /* Deparse operator name plus decoration. */
    deparseOperatorName(buf, form);
    appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");

    /* Deparse right operand. */
    arg2 = lsecond(node->args);
    deparseExpr(arg2, context);

    appendStringInfoChar(buf, ')');

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, ')');

    ReleaseSysCache(tuple);
}

/*
 * Deparse a RelabelType (binary-compatible cast) node.
 */
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
    deparseExpr(node->arg, context);
    if (node->relabelformat != COERCE_IMPLICIT_CAST)
        appendStringInfo(context->buf, "::%s",
                         format_type_with_typemod(node->resulttype,
                                                  node->resulttypmod));
}

/*
 * Deparse a BoolExpr node.
 *
 * Note: by the time we get here, AND and OR expressions have been flattened
 * into N-argument form, so we'd better be prepared to deal with that.
 */
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    const char *op = NULL;      /* keep compiler quiet */
    bool        first;
    ListCell   *lc;

    switch (node->boolop)
    {
        case AND_EXPR:
            op = "AND";
            break;
        case OR_EXPR:
            op = "OR";
            break;
        case NOT_EXPR:
            appendStringInfoString(buf, "(NOT ");
            deparseExpr(linitial(node->args), context);
            appendStringInfoChar(buf, ')');
            return;
    }

    appendStringInfoChar(buf, '(');
    first = true;
    foreach(lc, node->args)
    {
        if (!first)
            appendStringInfo(buf, " %s ", op);
        deparseExpr((Expr *) lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');
}

/*
 * Deparse IS [NOT] NULL expression.
 */
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;

    appendStringInfoChar(buf, '(');
    deparseExpr(node->arg, context);
    if (node->nulltesttype == IS_NULL)
        appendStringInfoString(buf, " IS NULL)");
    else
        appendStringInfoString(buf, " IS NOT NULL)");
}

/*
 * Deparse ARRAY[...] construct.
 */
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
    StringInfo  buf = context->buf;
    bool        first = true;
    ListCell   *lc;

    appendStringInfoString(buf, "ARRAY[");
    foreach(lc, node->elements)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        deparseExpr(lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ']');

    /* If the array is empty, we need an explicit cast to the array type. */
    if (node->elements == NIL)
        appendStringInfo(buf, "::%s",
                         format_type_with_typemod(node->array_typeid, -1));
}